NEW YORK (Reuters Health) - New research suggests that men who undergo surgery to remove their prostate as a result of prostate cancer may get a little less than they bargained for -- in terms of penis size, that is.

Researchers at the University of Miami in Florida found that men who underwent prostate-removal surgery, known as prostatectomy, experienced a slight decrease in the size of their flaccid and stretched penis. The length of the stretched penis approximates the length of an erect penis.

In most cases, the size difference was quite small. But in 20 percent of the study participants, penile length decreased by at least 15 percent.

Before undergoing prostatectomy, men should be told that they could walk away with a slightly smaller penis, study author Dr. Mark S. Soloway told Reuters Health.

"Probably men should be informed that it's a risk, so that they'll be prepared for it," he said.

The knowledge that prostatectomy can decrease penis size is very new, Soloway said, and the vast majority of men have likely never received any such warning before surgery.

"I think very few urologists, including myself, indicate to men that following prostatectomy, there may be a shortening of the penis," he noted.

The prostate, a gland located at the base of the bladder, contributes fluids to semen. Prostate cancer is the most common cancer in older men, but it only becomes invasive and life threatening in some.

In the Journal of Urology, Soloway and his team note that some men have reported a decrease in penis size following prostatectomy for prostate cancer, but little research has been dedicated to the concern.

To investigate this question, the researchers measured flaccid and stretched penile length, as well as circumference, in 124 men before prostatectomy and three months later.

All of these measures of penis size decreased after surgery, Soloway and his colleagues report.

Before surgery, the average flaccid penile length of the men included in the study was nine centimeters (3.5 inches) or longer, with an average stretched penile length of at least 13 centimeters (just over 5 inches).

After the procedure, however, the median flaccid penile length fell to eight centimeters, while the same value for stretched length dropped to 12.5 centimeters.

A total of 68 percent of participants showed a decrease in stretched penile length, with 19 percent experiencing a decrease in length of at least 15 percent.

Many study participants also reported a marked decrease in sexual functioning after prostatectomy, a known risk of the procedure, Soloway and his colleagues note.

While 92 percent of patients prior to surgery reported being able to achieve an erection, only 33 percent retained that ability three months later.

This marked impotence following surgery may, in part, explain the concurrent decrease in penis size, Soloway suggested -- with lack of use, the penis may shorten.

Other potential explanations include changes in the body that occur as a result of surgery to remove the prostate, he said.

Could knowing that prostatectomy may decrease penis size inspire some men to forgo the potentially life-saving operation?